1. Field of the Invention
The present invention relates to a test stand for accelerated testing of vehicle suspension components generally and focuses more particularly on testing the structural durability of vehicle wheels.
2. Background Art
Vehicles are extensively tested to verify compliance with durability standards and provide quality assurance. One vehicle durability test is known as a road durability test in which complete vehicle prototypes are driven on a variety of roads that provide different challenges to vehicle durability. Typical road durability tests may require 80 days of substantially continuous driving. This type of test is an excellent durability test and can provide valuable data to vehicle designers. One problem with this type of test is that it cannot begin until a prototype is fully constructed. Test results may not be available for an extended prior of time, potentially as long as or longer than 80 days, while the test is run.
Testing wheels in a road durability test is expensive and time consuming. Many vehicle families may offer 8 to 10 different wheel designs to provide model differentiation. Wheel and tire option packages are popular with consumers and add to the profit potential for new vehicle sales. Currently, original equipment manufacturers test vehicle wheels for quality assurance. One problem associated with testing 10 different wheels in long term road tests is that a large number of prototype vehicles are required for testing. Another problem is the substantial delay in obtaining approval of new wheels. Prototype vehicles are generally destroyed after road durability testing in the course of being deconstructed and analyzed. There is a substantial cost incurred when expensive prototype vehicles must be scrapped.
It is has been determined that the most damaging event for wheel road durability testing is a chuck hole impact. It is difficult to simulate accurately chuck hole testing in an accelerated test. Accelerated chuck hole testing requires simulation of a dynamic impact event which is a complex multi-variable simulation. While chuck holes in roads vary in size and shape, testing standards have been developed for simulating chuck hole impacts at various speeds. For example, chuck hole testing for driving at 30 miles per hour has led to the development of a standard chuck hole wherein a 4″ depth chuck hole is provided that is 30″ long. When a vehicle traveling at 30 miles per hour rides over the test chuck hole, the tire and wheel generally drop approximately 2″ by the time the edge of the chuck hole is contacted by the tire. The tire does not generally bottom out in the chuck hole.
All parts of a vehicle suspension assembly can impact the performance of a wheel in a chuck hole impact event. In addition to testing wheels, chuck hole testing may be used to dynamically test shocks, springs and other suspension components. To improve vehicle suspension design, there is a need for an accelerated testing procedure that will facilitate suspension tuning prior to the availability of completed vehicle prototypes.
Accelerated testing may be conducted on vehicle test tracks that may be provided with chuck hole test areas. Reliable accelerated testing may be provided by placing a series of test chuck holes in a test track environment and passing a vehicle repeatedly over the series of chuck holes. Accelerated testing on a test track is less time-consuming and may be less expensive than road durability testing, but requires relatively expensive test track driving time. Testing for wheel durability on such a test track may require up to 10 days to develop reliable durability test results. This approach to accelerated testing is a destructive vehicle test and requires expensive prototype vehicles.
Radial test machines have been developed for wheel and tire testing. Radial test machines allow accelerated testing of wheels and tires at relatively high speeds. A tire and wheel may be instrumented with strain gauges and other sensors and run on a rotating drum that is driven by a relatively low torque motor in a radial test machine. Simulating a chuck hole impact on a radial test machine is difficult due to the severity of a chuck hole impact. Chuck hole impact simulation for durability testing may necessitate a 5,000 to 6,000 pound radial load impact that may occur with a frequency of two impacts per second on a radial test machine. Normal radial test machines under such test conditions would be expected to self destruct.
One example of a test machine used to simulate an impact event is disclosed in U.S. Pat. No. 5,817,935. This patent discloses a test apparatus in which a wheel is rotated against a cylindrical drum or wheel that is provided with an obstacle having a relatively low profile. The wheel is supported on a hub that is rotated by a steering knuckle so that the tire remains in contact with the road wheel. If an obstacle equivalent to a 4″ deep chuck hole were provided on the test apparatus disclosed in this patent, the test apparatus is expected to be damaged or destroyed. Another shortcoming of this device is that it is not capable of being used to test other suspension components.
Another approach to simulating impact resistance of a tire is disclosed in U.S. Pat. No. 3,986,392 wherein a plunger is periodically extended through a peripheral opening in a test wheel to cause an impact event on the tire. The tire is relatively rigidly supported on a frame as it engages the test wheel. The test device would not be expected to be able to withstand repeated impacts of the severity that could provide reliable wheel durability testing. This apparatus is also not capable of testing other suspension components dynamically.
There is a need for an accelerated wheel test that also may be used to test other suspension components. Such an accelerated test must provide reliable durability data to verify that a wheel suspension component is capable of withstanding rapidly repeated 5,000 to 6,000 pound radial loads representing simulated chuck hole impact events without damage to the test equipment. There is also a need for a reliable chuck hole impact event durability test apparatus that does not self-destruct.
The above problems with prior art durability testing and accelerated durability testing are addressed by applicant's invention as summarized below.